The field of the present invention relates to devices for modulating, routing and/or processing optical signal power transmission. In particular, optical waveguides and resonators for integrated optical devices, as well as methods of fabrication and use thereof, are disclosed herein. The waveguides and resonators include a multi-layer laterally-confined dispersion-engineered waveguide segment, and may further include one or more active layers, thereby enabling tailoring of optical properties of the waveguide/resonator, and/or controlled modulation thereof.
This application is related to subject matter disclosed in:
A1) U.S. provisional Application No. 60/111,484 entitled “An all-fiber-optic modulator” filed Dec. 7, 1998 in the names of Kerry J. Vahala and Amnon Yariv, said provisional application being hereby incorporated by reference in its entirety as if fully set forth herein;
A2) U.S. application Ser. No. 09/454,719 entitled “Resonant optical wave power control devices and methods” filed Dec. 7, 1999 in the names of Kerry J. Vahala and Amnon Yariv (now U.S. Pat. No. 6,633,696), said application being hereby incorporated by reference in its entirety as if fully set forth herein;
A3) U.S. provisional Application No. 60/108,358 entitled “Dual tapered fiber-microsphere coupler” filed Nov. 13, 1998 in the names of Kerry J. Vahala and Ming Cai, said provisional application being hereby incorporated by reference in its entirety as if fully set forth herein;
A4) U.S. application Ser. No. 09/440,311 entitled “Resonator fiber bi-directional coupler” filed Nov. 12, 1999 in the names of Kerry J. Vahala, Ming Cai, and Guido Hunziker (now U.S. Pat. No. 6,580,851), said application being hereby incorporated by reference in its entirety as if fully set forth herein;
A5) U.S. provisional Application No. 60/183,499 entitled “Resonant optical power control devices and methods of fabrication thereof” filed Feb. 17, 2000 in the names of Peter C. Sercel and Kerry J. Vahala, said provisional application being hereby incorporated by reference in its entirety as if fully set forth herein;
A6) U.S. provisional Application No. 60/226,147 entitled “Fiber-optic waveguides for evanescent optical coupling and methods of fabrication and use thereof”, filed Aug. 18, 2000 in the names of Peter C. Sercel, Guido Hunziker, and Robert B. Lee, said provisional application being hereby incorporated by reference in its entirety as if fully set forth herein;
A7) U.S. provisional Application No.60/170,074 entitled “Optical routing/switching based on control of waveguide-ring resonator coupling”, filed Dec. 9, 1999 in the name of Amnon Yariv, said provisional application being hereby incorporated by reference in its entirety as if fully set forth herein;
A8) U.S. Pat. No. 6,052,495 entitled “Resonator modulators and wavelength routing switches” issued Apr. 18, 2000 in the names of Brent E. Little, James S. Foresi, and Hermann A. Haus, said patent being hereby incorporated by reference in its entirety as if fully set forth herein;
A9) U.S. Pat. No. 6,101,300 entitled “High efficiency channel drop filter with absorption induced on/off switching and modulation” issued Aug. 8, 2000 in the names of Shanhui Fan, Pierre R. Villeneuve, John D. Joannopoulos, Brent E. Little, and Hermann A. Haus, said patent being hereby incorporated by reference in its entirety as if fully set forth herein;
A10) U.S. Pat. No. 5,926,496 entitled “Semiconductor micro-resonator device” issued Jul. 20, 1999 in the names of Seng-Tiong Ho and Deanna Rafizadeh, said patent being hereby incorporated by reference in its entirety as if fully set forth herein; and
A11) U.S. Pat. No. 6,009,115 entitled “Semiconductor micro-resonator device” issued Dec. 28, 1999 in the name of Seng-Tiong Ho, said patent being hereby incorporated by reference in its entirety as if fully set forth herein.
A12) U.S. provisional Application No. 60/257,218 entitled “Waveguides and resonators for integrated optical devices and methods of fabrication and use thereof”, filed Dec. 21, 2000 in the name of Oskar J. Painter, said provisional application being hereby incorporated by reference in its entirety as if fully set forth herein;
A13) U.S. provisional Application No. 60/257,248 entitled “Modulators for resonant optical power control devices and methods of fabrication and use thereof”, filed Dec. 21, 2000 in the names of Oskar J. Painter, Kerry J. Vahala, Peter C. Sercel, and Guido Hunziker, said provisional application being hereby incorporated by reference in its entirety as if fully set forth herein;
A14) U.S. provisional Application No.60/301,519 entitled “Waveguide-fiber Mach-Zender interferometer and methods of fabrication and use thereof”, filed Jun. 27, 2001 in the names of Oskar J. Painter, David W. Vernooy, and Kerry J. Vahala, said provisional application being hereby incorporated by reference in its entirety as if fully set forth herein; A15) U.S. non-provisional application Ser. No. 09/788,303 entitled “Cylindrical processing of optical media”, filed Feb. 16, 2001 in the names of Peter C. Sercel, Kerry J. Vahala, David W. Vernooy, and Guido Hunziker (now U.S. Pat. No. 6,888,987), said non-provisional application being hereby incorporated by reference in its entirety as if fully set forth herein.
A16) U.S. non-provisional application Ser. No. 09/788,331 entitled “Fiber-ring optical resonators”, filed Feb. 16, 2001 in the names of Peter C. Sercel, Kerry J. Vahala, David W. Vernooy, Guido Hunziker, and Robert B. Lee (now U.S. Pat. No. 6,891,997), said non-provisional application being hereby incorporated by reference in its entirety as if fully set forth herein.
A17) U.S. non-provisional application Ser. No. 09/788,300 entitled “Resonant optical filters”, filed Feb. 16, 2001 in the names of Kerry J. Vahala, Peter C. Sercel, David W. Vernooy, Oskar J. Painter, and Guido Hunziker (now U.S. Pat. No. 6,865,317), said non-provisional application being hereby incorporated by reference in its entirety as if fully set forth herein.
A18) U.S. non-provisional application Ser. No. 09/788,301 entitled “Resonant optical power control device assemblies”, filed Feb. 16, 2001 in the names of Peter C. Sercel, Kerry J. Vahala, David W. Vernooy, Guido Hunziker, Robert B. Lee, and Oskar J. Painter (now U.S. Pat. No. 6,891,996), said non-provisional application being hereby incorporated by reference in its entirety as if fully set forth herein.
A19) U.S. provisional Application No. 60/335,656 entitled “Polarization-engineered transverse-optical-coupling apparatus and methods”, filed Oct. 30, 2001 in the names of Kerry J. Vahala, Peter C. Sercel, Oskar J. Painter, David W. Vernooy, and David S. Alavi, said provisional application being hereby incorporated by reference in its entirety as if fully set forth herein;
A20) U.S. provisional Application No. 60/334,705 entitled “Integrated end-coupled transverse-optical-coupling apparatus and methods”, filed Oct. 30, 2001 in the names of Henry A. Blauvelt, Kerry J. Vahala, Peter C. Sercel, Oskar J. Painter, and Guido Hunziker, said provisional application being hereby incorporated by reference in its entirety as if fully set forth herein;
A21) U.S. provisional Application No.60/333,236 entitled “Alignment apparatus and methods for transverse optical coupling”, filed Nov. 23, 2001 in the names of Charles I. Grosjean, Guido Hunziker, Paul M. Bridger, and Oskar J. Painter, said provisional application being hereby incorporated by reference in its entirety as if fully set forth herein;
A22) U.S. non-provisional application Ser. No. 10/037,146 entitled “Resonant optical modulators”, filed Dec 21, 2001 in the names of Oskar J. Painter, Peter C. Sercel, Kerry J. Vahala, David W. Vernooy, and Guido Hunziker, said non-provisional application being hereby incorporated by reference in its entirety as if fully set forth herein.
This application is also related to subject matter disclosed in the following publications, each of said publications being hereby incorporated by reference in its entirety as if fully set forth herein:
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P8) E. L. Wooten, K. M. Kissa, and A. Yi-Yan, “A review of lithium niobate modulators for fiber-optic communications systems”, IEEE J. Selected Topics in Quantum Electronics, Vol. 6(1), 69 (2000);
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P12) M. L. Gorodetsky, A. A. Savchenkov, V. S. Ilchenko, “Ultimate Q of optical microsphere resonators”, Optics Letters, Vol. 21, 453 (1996);
P13) Carl Arft, Diego R. Yankelovich, Andre Knoesen, Erji Mao, and James S. Harris Jr., “In-line fiber evanescent field electrooptic modulators”, Journal of Nonlinear Optical Physics and Materials Vol. 9(1) 79 (2000);
P14) Pochi Yeh, Amnon Yariv, and Chi-Shain Hong, “Electromagnetic propagation in periodic stratified media. I. General theory”, J. Optical Soc. Am., Vol. 67(4) 423 (1977);
P15) Ming Cai, Oskar Painter, and Kerry J. Vahala, “Observation of critical coupling in a fiber taper to a silica-microsphere whispering-gallery mode system”, Physical Review Letters, Vol. 85(1) 74 (2000);
P16) M. Kondow, T. Kitatani, S. Nakatsuka, M. C. Larson, K. Nakahara, Y. Yazawa, M. Okai, and K. Uomi, “GaInNAs: A novel material for long-wavelength semiconductor lasers”, IEEE Journal of Selected Topics in Quantum Electronics, Vol 3(3), 719 (1997);
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Optical fiber and propagation of high-speed optical pulses therethrough has become the technology of choice for high-speed telecommunications. Generation of trains of such high-speed optical pulses, representative of voice, video, data, and/or other signals, requires high-speed optical modulation techniques, typically intensity modulation techniques. Direct intensity modulation of the light source (usually a laser diode) generally induces unwanted phase and/or frequency modulation as well, which may be problematic when the modulated optical mode must propagate long distances within the optical fiber, or when the modulated optical mode is one narrow-linewidth wavelength component among many within a wavelength division multiplexed (WDM) fiber-optic telecommunication system. It has therefore become standard practice to provide an external intensity modulator as a separate optical component, to act on a propagating optical mode after it has left the light source.
Other devices may be required for subsequent manipulation and/or control of the propagating optical pulse train, including but not limited to, for example, routers, switches, fixed and variable attenuators, fixed and variable couplers, bi-directional couplers, channel add-drop filters, N×N switches, and so forth. It is desirable for these devices to perform their respective functions without the need for conversion of the optical pulse train into an electronic signal for manipulation and re-conversion to an optical pulse train following manipulation. It is preferable for these devices to perform their respective functions by direct manipulation of the optical pulse train. To this end many of these devices are fabricated as integrated devices, with optical portions and electronically-driven control portions fabricated as a single integrated component. Many of these devices function by controlling flow of optical power from one optical mode to another optical mode in a controlled fashion. For example, optical power may be shifted from a propagating optical mode of a first optical fiber to a propagating mode of a second optical fiber in an actively-controlled fashion, using so-called directional couplers, or in a wavelength-dependent fashion (active or passive), using so-called channel add-drop filters. Application of a control signal to an active device may cause optical power to remain within a propagating optical mode of a first optical fiber, or to couple into a propagating optical mode of a second optical fiber.
High insertion losses associated with currently available devices necessitate use of optical amplifiers to boost optical signal levels in a fiber-optic telecommunications system, essentially to replace optical power thrown away by the use of lossy modulators, couplers, and other devices. This adds significantly to the cost, size, and power consumption of any fiber-optic system or sub-system. Furthermore, the full potential of powerful new on-chip integrated optical devices cannot be realized when a substantial fraction of the optical signal is lost through inefficient transfer of optical power between an optical fiber and a waveguide on an integrated optical chip.
Optical signal power transfer between various optical devices in a fiber-optic telecommunications system relies on optical coupling between optical modes in the devices. Transverse-coupling (also referred to as transverse optical coupling, evanescent coupling, evanescent optical coupling, directional coupling, directional optical coupling) may be employed, thereby eliminating transverse mode matching requirements imposed by end-coupling. Such optical power transfer by transverse-coupling depends in part on the relative modal indices of the transverse-coupled optical modes. Active control of the modal index of one or both of the transverse-coupled optical modes would therefore enable active control of the degree to which optical power is transferred from one device to the other, preferably using control voltages substantially smaller magnitude than required by currently available devices. Optical power transfer from a fiber-optic or other low-index optical waveguide to an integrated on-chip optical device (typically higher-index) could be greatly improved by employing transverse-coupling. Such optical power transfer could be actively controlled by controlling a modal index of an optical mode of a waveguide and/or resonator of the integrated device. Optical losses within such an integrated on-chip device could also be reduced.
FIG. 1 shows an example of a modulator 10 fabricated as an optical waveguide Mach-Zender interferometer on an electro-optic crystal substrate 12 (typically lithium niobate). Standard fabrication techniques are used to fabricate the waveguide 14 (usually lithographic masking followed by ion diffusion) and to deposit control electrodes 16. An incident optical signal propagating into entrance face 18 (i.e., “end-coupled”) and through the device is divided into the two arms of the interferometer waveguide 14, application of a control voltage across the control electrodes 16 (in any of several configurations) induces a relative change in the modal indices of the optical modes in the arms (by an electro-optic mechanism), and the optical signals propagating in the arms are then recombined before exiting through exit face 19. Variation of the control voltage enables modulation of the transmission of the incident optical signal from a lower operational optical transmission level (when the recombined optical modes substantially destructively interfere; preferably near zero transmission) to an upper operational optical transmission level (when the recombined optical modes substantially constructively interfere; preferably near 100% transmission, but typically limited by insertion loss of the modulator). Modulators of this sort are widely used in fiber optic telecommunications systems, may enable modulation frequencies up to several tens of GHz, and may require control voltages of at least several volts up to about 10 volts for substantially full modulation of the optical signal. The control voltage required for a device to achieve substantially full modulation (i.e., near zero transmission of the optical mode at the lower transmission level) is referred to as Vπ, since a phase shift of about π is required to make the optical modes propagating in the two arms of the interferometer substantially destructively interfere. Vπ is an important figure-of-merit for characterizing electro-optic modulators. The relatively high Vπ of typical lithium niobate modulators forces the use of expensive high speed electronic drivers (described below), increasing cost and power consumption of the device. In addition, coupling optical power into and out of the faces of the modulator (end-fire coupling, or end-coupling) is quite inefficient, and typical lithium niobate modulators may have insertion losses as high as 6 dB. Most of the insertion loss may be attributed to transverse mode mismatch of the input optical mode and the preferred mode of the waveguide. This may be somewhat mitigated by modifying the device to achieve better mode-matching, but at the expense of a larger Vπ.
FIG. 2 shows an example of a directional coupler 20 (also referred-to as a 2×2 optical switch) fabricated as an integrated optical device on an electro-optic crystal substrate 22 (typically lithium niobate). In this example two waveguides 24a and 24b are fabricated on the substrate, and are positioned in relatively close proximity in a coupling portion of the device. In this way an optical signal propagating in an optical mode of one waveguide may transverse-couple into an optical mode of the second waveguide. The device is typically constructed so that over the length of the coupling portion, substantially all of the optical power entering the first waveguide is transferred into the second waveguide. Control electrodes 26 are positioned so that an applied control voltage alters the relative modal indices of the optical modes of the two waveguides in the coupling portion (by an electro-optic mechanism). A switching voltage V0, typically several volts up to about 10 volts, is the voltage that alters the relative modal indices (i.e., the phase matching condition between the waveguides) to the extent that substantially none of the optical power entering the first waveguide is transferred to the second waveguide. By switching the control voltage between about zero volts and about V0, the optical power entering the first waveguide may be switched between exiting via the second waveguide (zero volts applied) or exiting via the first waveguide (V0 applied). Such couplers may exhibit switching frequencies of up to 10 GHz, and V0 is an important figure-of-merit for characterizing electro-optic couplers. In a manner similar to the modulators described hereinabove, these devices require costly high-speed electronic driver hardware (described below) and exhibit insertion losses as high as 6 dB.
A general discussion of electro-optic modulators, interferometers, and couplers may be found in Fundamentals of Photonics by B. E. A. Saleh and M. C. Teich (Wiley, N.Y., 1991), hereby incorporated by reference in its entirety as if fully set forth herein. Particular attention is called to Chapter 18.
For operating voltages (Vπ or V0) on the order of several volts and high modulation/switching frequencies, a high speed electronic control input signal must typically be amplified to the appropriate level for application to the device by a high speed electronic amplifier, usually referred to as a driver or RF driver. A driver adds substantially to the size, cost, and power consumption of current optical modulators, couplers, and other devices, and may limit the maximum frequency at which such devices may be driven. For operating voltages (Vπ or V0) on the order of 10 V, a device may consume on the order of 1 W of electrical drive power. This power must be dissipated and/or otherwise managed properly to avoid overheating, degraded performance, and/or eventual failure of the device. This may be particularly problematic when the properties defining the performance of the device (such as waveguide pathlength, refractive and modal indices, and so forth) are temperature dependent. Since such large numbers of such modulators, couplers, switches, and other optical devices are required to implement a fiber-optic telecommunications system of any significant extent (organization-, city-, state-, nation-, and/or world-wide; alternatively enterprise, metro, and/or trunk systems), any potential reductions in size, cost, and/or power consumption may prove to be quite significant. A sub-volt control voltage level (Vπ and/or V0) would eliminate the need for a driver, potentially cutting the cost of each device, and would result in a corresponding decrease in power consumption and its attendant technical difficulties and economic disadvantages. Limitations on operating speed imposed by driver performance would be eliminated.
It is desirable to provide optical modulators, interferometers, couplers, routers, add/drop filters, switches, and/or other devices wherein optical power may be efficiently transferred to/from the device from/to an optical fiber or other low-index waveguide without limitations and/or insertion losses imposed by end-coupling. It is desirable to provide optical modulators, interferometers, couplers, routers, add/drop filters, switches, and/or other devices wherein optical power may be efficiently transferred to/from the device from/to an optical fiber or other low-index waveguide by transverse-coupling. It is desirable to provide optical modulators, interferometers, couplers, routers, add/drop filters, switches, and/or other devices having insertion loss less than about 3 dB. It is desirable to provide optical modulators, interferometers, couplers, routers, add-drop filters, switches, and/or other integrated optical devices that may be well modal-index-matched to optical fiber and/or other low-index waveguides. It is desirable to provide optical modulators, interferometers, couplers, routers, add-drop filters, and/or other devices that may be fabricated as integrated optical devices, on a planar platform or on multiple-level vertically-integrated planar platforms. It is therefore desirable to provide optical modulators, interferometers, couplers, routers, add-drop filters, switches, and/or other devices wherein the required control voltage level (Vπ or V0) is less than about one volt. It is desirable to provide optical modulators, interferometers, couplers, routers, add-drop filters, and/or other devices that do not require a driver for amplifying electronic control signals. It is desirable to provide optical modulators, interferometers, couplers, routers, add-drop filters, and/or other devices that are compatible with other extant components of a fiber-optic telecommunications system.